The surprising discovery of the first set of double pulsars in the Universe updates research published just a month ago.

An international team of scientists announced their find yesterday at the Binary Radio Pulsars meeting in Colorado in the U.S.

In December the researchers led by Dr Andrew Lyne, director of the UK's Jodrell Bank Observatory, reported in the journal Nature the discovery of a pulsar and a super fast neutron star orbiting each other.

But when they re-examined the data from CSIRO's Parkes telescope in Australia, they were surprised to find the neutron star was actually a pulsar.

The double pulsars are in the near neighbourhood of the Milky Way and were first seen in the middle of last year.

But researchers originally missed the second pulsar because its beam was hidden by the first pulsar as the two rapidly rotated. This lack of a series of extremely regular beams of radio waves led the researchers to assume this second object was a neutron star.

"One of the features of the system is that the two pulsars almost eclipse each other as they rotate. At first observation, one of the pulsars was behind the other one and we couldn't see it. Around November one of our collaborators noticed a second pulse coming 2.8 seconds behind the first.

"It's pretty much like a lighthouse. If a lighthouse was sending a signal out to the horizon a ship would see it, but an aeroplane above it would only see the circle of illumination, it wouldn't see the beam. That's basically what we think happens with this pulsars. There may be many neutron stars that are really pulsars whose beam we can't see."

Like neutron stars, pulsars contain a large amount of matter squashed into a relatively small space. Reynolds said the density was equivalent to compressing the entire Earth into a few centimetres.

Future research

Australian team member Dr Richard Manchester of CSIRO's Australia Telescope National Facility said the double pulsar formed an excellent natural laboratory.

The pulsars will provide an opportunity for proving aspects of Einstein's theory of general relativity. This would include the occurrence of gravitational waves, thought to distort time and space around extremely massive objects, the researchers said.

The enormous gravity exerted by the two pulsars would eventually cause them to merge into a black hole, producing a massive explosion. The orbital energy from the system will be lost in the form of Einstein's elusive gravity waves.

Evidence of the pulsars merging could be evident in just a few years, Reynolds said.

Astronomers could also study aspects of the pulsars' spin, which is thought to be like a wobbly spinning top.